Communication system



' Och-3, 19 39. H; J. NICHOLS 3 7 COMMUNICATION SYSTEM Original Filed July 21, 1934 2 Sheets-Sheet 1 A TTORNEYS.

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' COMMUNICATION SYSTEM Original Filed July 21, 1934 2 Sheets-Sheet 2 m M2. H 9.

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- Patented Oct. 3, 1939 UNITED STATES COMMUNICATION SYSTEM Harry J. Nichols, Binghamton, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Original application July 21, 1934, .Serial No.

736,383. Divided and this application Septemher 2, 1937, Serial No. 162,122

'1 Claims. 7 (Cl. 14-289) This invention relates to synchronizing systems and more particularly to synchronizing apparatus employed in such systems for remotely controlled communication apparatus.

The present invention is a divisional application of the copending application Serial No. 736,383, filed July 21, 1934, now Patent #2,111,153. The invention claimed in the said copending application relates solely to a specific type of syn.-

chronlzing system in which the transmitted periodic impulses are adapted to control release means associated with the receiving rotary member, thereby permitting synchronism to be established between the transmittingand receiving 15 rotary members to maintain such phase condition or, in the event of departure therefrom, to

correct the phase condition between the two,

members to establish unison therebetween.

The invention claimed in the present application relates solely to the apparatus provided to effect the phase correction or phase maintenance features of the system and comprises an apparatus which is accurate, positive, quiet, andreliable in action and which, is equally adaptable to systems using isonchronous driving means and systems in which'minor variations in the driving means are likely to occur.

Another feature of. the present invention" claimed herein resides in the novel planetary phase corrector mechanism suitable to such methods employed in characterizing communication synchronizing systems.

' Further objects of the instant invention reside in any novel feature of construction or operation or novel combination of parts present in the embodiment of the invention described and shown in the accompanying drawings whether within or without the scope of the appended claims and irrespective of other specific statements as to the scope of the inverl'tion contained herein.

In many communication systems, such as in television, facsimile, and printing telegraph sys-.

tems, wherein images, pictures, and writing are 5 transmitted by electrical means, it is essential that time and phase .synchronism be established and maintained between certain elements of the apparatus at the sending and receiving stations. For example, in certain television systems, a roso tating scanning disk is utilized to scan the subject at the sending station and a similar element is utilized-at the receiving station to reproduce the subject ,in the same order of scanning. Like wlsein facsimile systems, a device which in-. 5 cludes a rotating cylinder, commonly called the analyzer, is utilized at the sending station to scan the elemental areas of the subject and a corresponding device, commonly called the repro-- ducer, is utilized to reproduce these elemental areas inlike order at the receiving station. And

in. synchronous printing telegraph systems, rotary distributors at the sending and receiving stations are utilized to coordinate the transmission and 'The method used to establish and maintain the sending andreceiving devices at the same speed and proper phase relation is called synchronization. The present invention relates to methods and apparatus for. automatic synchronization applicable to systems of various types wherein synchronized rotating sending ments are used.

In the figures:

Fig, 1 shows in diagrammatic form a sending rotary distributor of a typical printing telegraph system, illustrating one means of generating periodic synchronizing signals.

. Fig. 2 shows in similar manner the synchroniz-' ing control circuits at the receiving rotary distributor of a typical printing telegraph system illustrating one method of utilizing periodic syn-' chronizi'ng signals to produce synchronism.

Fig. 3'shows a side view in part section of an epicyclic or planetary phase corrector mechanism in accordance with the invention as applied to a rotary contactor such as is used in synchronous printing telegraph systems.

and receiving elecorrector mechanism offi ig.- 3, the section being taken along line 44 of Fig. 3.

Fig.5 "shows another embodiment of the invention as applied to the sending end of a facsimile system.

Fig. 6 shows in diagrammatic form the invention' applied to the receiving end of a facsimile system.

Fig. '7' shows a-viewsimilar to that of Fig. 3 illustrating an embodiment of the invention as appliedto the facsimile system of Fig. 5.

Fig. 8 shows a plan-viewin' section of the mechanisfn of Fig. 7 the section being taken along lined-B of Fig. 7.

Fig. 9 shows'in diagrammatic form means of generating periodic synchronizing signals .particularly adapted to the sending end of a television system.

Fig. 10 shows in diagrammatic form the synchronizing control circuits at the receiving end of a television system, illustrating another method of utilizing periodic synchronizing signals in accordance with the invention.

Fig. 11 shows an adaptation of the planetary phase corrector mechanism of Figs. 3 and 7 as applied to the synchronization of a television receiving scanning disk.

In the various figures, like characters designate like parts.

The synchronizing system of the invention comprises in general methods for automatically establishing and maintaining time and phase synchronism between remotely situated rotating elements, and a novel planetary phase corrector mechanism suitable to these methods and characterizing the system. The general method consists' at the sending end in generating and transmitting periodic signal impulses relating to a particular phase position of a rotary controlling element, and at the receiving end, in receiving and utilizing these signal impulses to automatically. establish synchronism of the rotary controlled element, and thereafter utilizing the periodic impulses to correct, when necessary, the

shows in diagrammatic form a typical rotary distributor used for sending synchronizing and printing signal impulses in a synchronous printing telegraph system. The distributor includes a rotary contactor RC comprising the controlling element in the system, and sweeping at uniform speed over the face of stationary commutator consisting of a segmented ring SR, comprising a plurality of separate insulated segments and a common ring CR. A particular segment, called the synchronizing segment .and designated by SS, sends a synchronizing signal to the line once,

for every rotation of contactor RC as follows:

One side of local battery Bis connected to one line terminal, the otherto the common ring CR; the other line terminal is connected to segment SS. Hence every time contactor RC passes over SS, a signal of definite duration and of predetermined time relation is generated .and sent to the line. The remaining segments are used to transmit printing signals and for other purposes, but

the present invention is not concerned with the printing functions of .the apparatus, hence they will not be described.

The synchronizing signals from the sending or controlling station are transmitted to the receiving station over any desired communication channel, such as a wire, or radio system, shown for simplicity as a two-wire line.

Referring now to Fig. 2,, the synchronizing signals when received are applied to a suitable receiving instrument, such as line relay R, of quick-.

acting, quick-release type. The contacts of relay R'arein circuit. with a local current source such as battery B, so that local current pulses corresponding to the received signals are produced in the local circuits by the closing and opening of the contacts of R. One side of battery B is connected-to the contacts of- R and thence to a bus from which multiple circuits connect various items of apparatus to the respective segments of ring SR. The circuit connected'to the synchronizing segment SS includes the winding of release magnet RM, of quick-acting slowrelease, pulse-sustained type, adapted to release rotary contactor RC when energized. For illustrative purposes, the release member 30 actuated by RM is shown in engagement with RC. A relay or magnet suitable for use as a release magnet is described in detail in my copending application, Serial No. 672,161, filed May 22, 1933. On either side of the synchronizing segment are located corrector segments designated by SI and S2, having corrector magnets MI and M2 connected in series therewith as shown.

The operation of the apparatus just described is as follows: Contactor RC, which comprises the controlled element of the system, is assumed to ing on into contact with SS during the latterpart of the local current pulse. MI is thus energized, causing RC to be advanced in phase by phase corrector means presently to be described. RM

is reenergized and sustained by the latter part of the local current pulse, hence remains operated'and'does not interfere with the rotation of RC. On successive synchronizing signals, RC is advanced by the phase corrector until the entire synchronizing pulse is received on SS, thus establishing perfect synchronism or unison, in which condition the energy of the synchronizing pulse goes entirely to sustain RM.

Thereafter, should RC contact with SI during the occurrence of the synchronizing pulse, MI is energized and the phase of RC is advanced to restore unison; should RC contact with S2, M2 is energized and the phase of RC is retarded to restore unison. Thus synchronism is maintained by correcting, whennecessary, the phase of RC, without altering the speed of the driving means synchronizing signals are transmitted over the same system as the printing signals, all signals are subject to the same retardation, and practical unison of the printing signals is assured by maintaining unison through the medium of the synchronizing signals.

Summarizing, the method of synchronizing illustrated by Figs. 1 and 2 consists of the steps of generating and transmitting single periodic Sig-- diameter, mounted thereon side by side.

are loose thereon. Drive gear GI is provided with a hub 2 on which is rotatably mounted epicyclic train arm 5. Collar 3, which maintains arm 5 in place, encircles hub 2 abutting against tracted. Likewise corrector magnet M2 has a a shoulder thereon, and is secured in position by a set screw 4 which extendsthrough hub 2 and bears against drive shaft I. Gear G3 is provided with a short hub on which is rotatably mounted epicycle arm 8.. A friction cup 9, containing a friction washer II] of fibrous material, is mounted upon the hub of G3, being held against rotation relative to G3 by pin II. The driven part, as for example hub I2 upon which rotary, contactor RC is mounted, is rotatable on drive shaft I, being driven by. the friction washer III. A tensioning nut I3, screwed on the threaded end of drive, shaft I, holds the assembly in position on the drive shaft and provides a means for adjusting the frictional force. A set screw I4 locks nut I3 in'the positionto which adjusted.

Pinion gear PI, called the first pinion, is ro tatably mounted on arm 5 by any suitable means,

such as shoulder rivet 6, so as to mesh properly with GI and the lowerpart of G2. In like man ner pinion gear P2, called the second pinion, is rotatably mounted on arm 8 so as to mesh properly with G3 and the upper part of G2, there being a slight clearance space between the two pinions.

Arm 5 is provided with a stop member or finger 5a, while arm 8 is provided with a like member 8a. Corrector magnet MI,of any suitable design, has a .plunger positioned to interceptfinger 5a when extended and to release same when replunger adapted to intercept and release fin- "ger 8a.

Gears GI and G3 preferably have the same number of teeth, and the same pitch diameter. Gear G2 preferably has the same pitch diameter as gears GI. and G3, but is provided with a different number of teeth, say one more or one less tooth. For example, let GI and G3 have teeth while G2 has 121 teeth. Pinions PI and P2 preferably have the same number of teeth, say 30, although this is immaterial. In such a gear system, the angular lead or lag per revolution of the driven gear relative to the drive gear is equal to I 36 0 1 Nix:

where N is the number of teeth in the drive gear and n is the number of teeth more or lessof the driven gear as compared to the drive gear. Therefore, in the example chosen, the lag of G2 as compared with GI is equal to approximately, while the lead of G3 as compared to G2 is equal to v calculated :by the general formula:-The speed. of the final gear .isequal to the speed of the first gear times the product of the teeth of all the drive gears divided by the product of the teeth of all the driven gears The operation of the phase corrector mechanism is as follows: Assume. that drive shaft I is in rotation while arms 5 and 8 are held against rotation by MI and M2 respectively. Then' for each revolution of the drive shaft, gear GI'progresses 120 teeth, and since pinion PI meshes with both GI and G2, G2 will likewise progress 120 teeth. Also since pinion P2 meshes with G2 and G3, G3 will progress 120 teeth; therefore, the driven member will rotate at the same speed as the drive shaft.

Now assume that with the drive shaft still in rotation, magnet'MI is energized, releasing arm 5. Then arm 5 is set in rotation with GI and G2, while pinion PI ceasesrotation, in efi'ect lock- 3 ing GI and G2 together, thus preventing any relative motion between them. During-this revolution, G2.progresses 121 teeth and since P2 meshes with G2 and G3, G3 likewise progresses 121 teeth. This representsa gain of one tooth pitch for G3, or a phase angle advanceof 3 degrees. The arm 5 may also be stopped at'a fractional part of the revolution to obtain a lesser phase angle change. Hence the driven member advances a like amount in phase with respect to the drive shaft; Assuming that at the end of the revolution, arm 5 is intercepted by MI and stopped, the driven mer n-- ber resumes rotation atthe same speed as the phase, and by releasing arm 8, the driven memher is cau'sed to lose onlag in phase. Mlfand M2 are thus, in eflect, triggers which select ,the'

direction in which the-phase correction is -t'o be applied. The changejin. phase is quitefgradual,

and the applicationofthe driving force'b'etween the drive shaft andgdriven member is continuous during the process of phase correction, the energy for the correction being obtained from the driving means. The change inphase of the' drivenmember per revolution of the drive shaft is indepe ndent of the speed of the drive shaft and is entirely a matter of the gear arrangement'used, a greater or less phase change being readily ob- V tainable by proper selection of the gear train.

The change in phase resulting from each corrective action may also be varied by arranging for the released member to be stopped after a fractional part of a revolution.

Since the phase correcting process is a matter of relative motion between arm 5 and arm .8, another way to obtain correction is to permit arms- 5 and B 'to revolve freely as a normal conditio'ny-an'd retard or stop one arm or the other.

when. correctionis desired. Such a method of phase correction is quite feasible and clearly within the scope of the invention, the method her'eidescribed being preferred mainly because of simplicity {as regards the operation of the cor- 1 rector-magnets.

In "applications where phase correction in one direction only is required, i. e. the phase'is' either to be advanced .arretarded but not both, th r-- gear arrangement maybe further simplified. For

' example, infacsimile -systems, it' is sometimes preferrd to use stop-start unison control where by the receiving .drum is arranged to rotate slightly faster than the sending drum, and at the end vof each revolution the receiving drum is retained momentarily until released in response to a synchronizing signal. It will be apparent that a selective differential speed increment in one direction may be obtained by a drive gear, a driven gear, and an epicyclic arm carrying a pinion constitute a differential spur gear, while surface of the subject matter.

the three gears and two pinions constitute a compound difierential spur gear. When an epicyclic arm is held, its pinion functions in the differential gear train to .efi'ect differential driving relation of its two associated gears, but when released it'functions as a planetary clutch. The system as a whole-may be termed a planetary transmission.

It is to be understood that wide variations in the arrangement and form of the gears, the gear ratios, the construction of the epicyclic arms, and the means for controlling the release andstopping of the epicyclic arms may be found convenient in adapting the invention to various synchronizing systems, and such variations will readily be perceived by those skilled in the art and are within the scope of the invention.

Referring now to Fig. 5 which shows in diagrammatic form the elements of the synchronizing apparatus in'accordance with the invention applied to a typical facsimile system, drive motor 20 is provided with a reduction gearbox 20a whereby the speed of drive shaft 2E is suitably reduced to drive rotary cylinder 22 at a lesser speed than the drive motor, as is usually' found to be desirable. The subjectmatter to be analyzed is mounted on rotary cylinder 22'. There are various known means for translating the light values of the subject matter into electrical r variations. One form of translating means commonly'used is shown. -A beam of light from a light source 23 is focused by optical means indicated by 24 upon a spot on the surface of the subject matter. A collector lens 25 collects the light reflected from the surface of the subject and focuses same upon a photo-cell 26. By causing the translating apparatus to be moved in translation, as indicated, it is evident that the combined rotary and translation movements will cause the light spot to 'pass progressively over the curved surface of the cylinder, and thus the elemental areas of the subject matter will be scanned. fI'he current passing through a photocell is proportional to the amount-of light which .it receives, hence the current therethroughvaries with the amount of light reflected from the variations are amplified by a suitable amplifier, indicated by 21, and are then transmitted over a communication channel, shown as 'a transmission line, to'the receiving station.

Because of the high degree of amplification required to increase the amplitude of the current variations in the photo-cell to values adequate for transmission, it is preferable in facsimile transmission apparatus to avoid the use of circuit interrupting devices such as -commuta-' tors and breaker contacts. Hence it is preferred that motor be of non-commutating type, prefapparatus.

These current erably a synchronous motor. For the same reason, while any suitable means may be used, I prefer to generate the periodic-synchronizing im pulses by non-commutating means, and to that end employ means including the rotary cylinder 22 and the translating device ofthe facsimile A strip or stripe 28, of suitable width, is placed over or on the subject matter mounted on the cylinder, the reflecting properties of the strip preferably representingv one of the extremes of light value, such as black or white. The strip is mounted out of the field of the subject matter, the preferred arrangement being a narrow black strip, somewhat shorter, than the cylinder, clamped along the length of the cylinder and serving also to hold the overlapping edges of the sheet containing the subject matter securely in place.

The synchronizing signals are generated as follows: The rotary cylinder 22 is put in rotation, and the translating device is brought into position at the margin of the field of the subject matter and the translating apparatus rendered operative. Thereafter, during the sending operation, a signal of definite duration is generated each time strip 28 passes beneath the light spot by reason of the current'variation produced in the photo-cell, which current variation, after amplification, is transmitted to the receiving station. This signal, transmitted for every revolution of cylinder 22, constitutes the synchronizing signal.

It is assumed that duplicate mechanism is provided at the sending and receiving stations. When receiving, the received synchronizing signals are utilized to establish and maintain synchronism as follows: Between the'motor drive shaft 2| and cylinder 22 is interposed a planetary phase corrector and clutch mechanism, designated by CM, to be described in connection with Figs. 7 and 8. On the hub of cylinder 22 adjacent the planetary mechanism is mounted 'a rotary contactor RC, sweeping over the stationary commutator 29 consisting of a common ring CR, and a segmented ring SR, shown diagrammatically inFig. 6. SR has four segments, namely a synably of the same angular width as the strip generating the synchronizing signal. Corrector magnets MI and M2 are connected respectively to segments SI and S2, and the segment BS is connected to RP representing the facsimile reproducing device, which, however, does not form a part of the present invention and need not be described. Relay .R receives the synchronizing and picture signals and is of suitable construction to translate same into local impulses of the proper characteristics as described in connectid; with Fig. 2.

Referring now to Figs. 7 and 8, which show in detail the mechanism designated by CM in Fig. 5, the planetary phase corrector, gears GI, G2 and G3 and magnets MI and -M2 are similar to those shown in Figs. 3 and 4 and do not require detailed description. Rotatablyv mounted on drive shaft 2| adjacent gear G3 and fast thereto is gear G4 forming part of the epicyclic clutch mechanism. Rotatably mounted on shaft 2| next to gear -(3A is bell crank 3| having a center boss 3la upon which a hub 32 is mounted and adjustably fixed as to rotation by suitable l 33b and a resilient rim 33a, preferably of firm exterior surface, and held in engagement with means, such as a set screw. Hub32, upon which cylinder 22 is mounted, is rotatable with respect to drive shaft 2| and is restrained from axial movement by a nut (notshown) on the outer end of drive shaft 2|. Contactor arm RC extends radially from hub 32, and sweeps over the face of stationary commutator 29.

Bell crank 3| carries on one arm pinion P3, rotatably mounted thereon, having a coupling wheel 33 fast on its shaft. Coupling wheel 33 has a metal core rubber, securely attached to the core. Mounted pivotally on the other arm of bell crank 3| is the coupling member or pawl 34, provided with arcuate end piece 340 lightly serrated on the coupling :wheel 33 by tractilespring 35. Pawl 34 is also: provided witha toe piece 34a extending radially and adapted to be engaged by armature 300irelease magnet RM, or suitable intermediary mechanism. The outward movement of pawl 34 is limited by heel against stop pin 36. The operation of the epicyclic clutch mechanism is as follows: Refer to Figs. '7 and 8 and assume that release magnet RM is not energized, hence armature 30 is in a position to'intercept piece 341) striking toe piece 34a. When toe piece 340; strikes armature 3'0, pawl 34 is forced ,out of engagement with coupling wheel 33. The light friction on hub 32 due to the rotation-of drive shaft 2| suffices to keep pawl 34 out of engagement with coupling wheel'33, leaving pinion P3 free to rotate. Further motion of hell crank 3! is thus arrested,

, and hub 32 remains stationary with contactor RC in contact with the. synchronizing segment SS of the stationary commutatoras illustrated in Fig. 6.

Now assume that armature 30 is withdrawn by reason of asynchronizing pulse energizing RM, thus releasing toe piece 34a; then tractile spring 35 snaps pawl 34 into engagement with coupling wheel 33.

carry end piece 380 along with it, this tendency being aided by the serrated surface. The sum of the radius of the coupling wheel 33 and that of the arc of motion of end piece 340 being greater than the center distance between the pivots of The coupling action is rapid and positive, slipping being'negligible, being equivalent to that of a pawl with a ratchet wheelwith an infinite number of teeth. The-coupling is accomplished L practically without shock and noise.

ffAt 'the meceiving station, in: the absence of chronizing strip 28.

The method of establishing and maintaining synchronism is as follows:

At the sending end, as shown in Fig.5, the analyzing device is placed-in position at the outer end of the drum 22 so that the scanning spot shines on the drum beyond the end of the syn- Motor 20 being started, a local control circuit (not shown) is closed, energizingrelease magnetRM, and holding same in operated condition. The epicyclic clutch is thus released, setting drum 22 into rotation, and starting the traverse of the analyzing device. When the scanning spot reaches the end of strip 28, synchronizing signals are-sent to the line.

synchronizing signals, release .magnet RM is unenergized, hub 32 is uncoupled from the drive Coupling wheel 33 being in rotation -counterclockwise as indicated. in Fig. 8, tends to shaft, drum 22 is stationary, and contactor RC is held at rest on the synchronizing segment as indicated in Fig. 6. When the first synchronizing signal is received, RM is energized, releasing the epicyclic clutch arm as previously described, setting drum 22 in motion. A'slight delay occurs in energizingRM and in the clutching operation, hence at the end of the first revolution of the receiving apparatus, it may be assumed that ccntactor RC is in contact with corrector segment SI when the synchronizing pulse occurs. Correctormagnet MI is thus energized, releasing arm 8, and advancing the phase of contactor RC.

These phase corrections are repeated until perhence the synchronizing signals do not reach the reproducer device, nor do the printing signals reach the release or corrector magnets, and hence there is no interference between synchronizing and printing operations.

To summarize, the method of establishing and maintaining synchronism in the facsimile system embodiment of the invention is the same as in the printing telegraph system embodiment. In the facsimile system embodiment, an epicyclic clutch mechanism is shown in preference to the friction drive of the printing telegraph system mainly because,as a rule, the drum bf the facsimile apparatus will be heavier than the rotary contactor of the printing telegraph apparatus, and hence requires more force in starting. It is to be understood, however, that the use of a clutch mechanism is a matter of preference, and under suitable conditions, a friction or other suitable drive may be used in conjunction with the planetary phase corrector in facsimile systems. a t,

In television systems, as in facsimile systems, where photo-cell pick-up and amplifiers are used,

it is usually preferable, to avoiduse of contactors in generating signal impulses. Fig. 9 shows a method of generating synchronizing impulses using a photo-cell pickup. A source of light 433 is positioned so as to concentrate a beam of light on a. scanning disk 60, having a synchronizing aperture. Mapositioned out of thefield of the picture scanning apertures tllb. A condenser le'ns 45 concentrates the beam of light, after passing through the aperture of the scanning member, upon a photo-cell, the current from which is amplified by amplifier 41 before passing to the outgoing transmission system.

Assuming the scanning member 40 to be in uniform rotation, a synchronizing signal is generated and transmitted once for each rotation of the scanning member, and at a particular manner described. in connection with Fig. 5.

Referring to Fig. 10, at the receiving station the incoming synchronizing signals, after suitableamplification, areapplied to a local circuit, one

segment SI occupying almost 180 of arc onthe' stationary commutator. The. other branch cirphase position of the scanning'member, in the,

6' cuit passes through the-winding of corrector magnet M2, and thence to half-ring segment.

S2. A rotary contactor RC (mounted on the hub of the scanning disk of Fig. 11) sweeps over the face of the stationary commutator as indicated.

The scanning element of a television receiver, whether in the form of a disk, drum, belt, or mir-" ror wheel, rotates at high speed, and is likely to have a sizable amount of rotational energy. Hence it is preferred to arrange for the receiving scanning element to rotate continuously, and graduallyiestablish.synchronism by bringing the scanning element from any out of phase position into unison, and thereafter make gradual phase by'which synchronization according to the invencorrections to maintain synchronism. Fig. 11 in connection with Fig. 10 shows the arrangement tion is obtained.

The phase correcting mechanism comprises gears ,Gl, G2 and-G3, arms 5 and" 8, pinions PI [and P2, and corrector magnets MI and "M2, the

structure being identical with that described in connection with Figs. 3 and 4. A hub 12 is mounted securely on the hub or gear G3 by suitable means such as a set screw, but is rotatable upon drive shaft 4!. Thescanning device, such as scanning disk 40, is mounted securely on hub 32 by suitable means. A nut 48 on the end of drive. shaft 4i holds the assembly in position.

Rotary contactor RC is also mounted on hub 42,

ahd sweeps over the face ofthe stationary coma mutator shown in Fig. 10.

The operation of the apparatus shown in Figs. 10 and 11 is as follows:

Assume that drive shaft H is in rotation at the speed of the drive shaft of the sending scanning disk shown in Fig. 9. Then for each revolution of the sending scanning disk, a synchroniz-v ing signal is transmitted, and upon reception at the receiving station, is amplified and applied to the local circuit shown in Fig. 10. It may also be assumed that picture signals-are transmitted aperiodically between the periodic synchronizing signals! The picture signals are, however, separated from the synchronizing signals by filters or other known means, so that only the periodic synchronizing signals are eifective to operate the corrector magnets and relay of Fig. 10. Assume that the first synchronizing signal is received when the rotary contactor is in contact with halfring segment S1. Corrector magnet Ml is there-.

. fore energized, releasing epicyclic arm .5, and as described in, connection with Figs. 3 and 4, causes the phase oi the scanning disk to be advanced a predetermined amount, say 3 degrees. 0n subsequent signals, a like advance in phase occurs each time MI is energized until rotary contactorRC is advanced until it contacts the section of insulation between segments SI and'SZ (shown at the Y unison point. Thereafter, phase corrections will only occur when RC shifts from unison and contacts either SI or $2; thus the phase of RC is corrected as necessary to maintain unison. The insulation between the corrector segments Si and S2 opposite the unison point is held to a minimum, making it impossible for unison to be established at the wrong point.

, It is to be observed that in the method disclosed for establishing synchronism of the television scanning device, the receiving rotary element is brought into unison from any out of phase position withthe least number of corrective steps possible under the circumstances. Assuming 9. 3 phase correction per revolution, 60revolutions would be required to establish unison from the extreme out of phase positionfi Since the usual speed for scanning devices is revolutions per second it follows that synchronism can be established in three seconds or less, with this particular'phase correction.

It will be evident from the foregoing that the system disclosed provides great flexibility in application and operation. For example, in the printing telegraph and facsimile application, the receiving machine or machines may be left running in ready condition, and when the sending machine starts sending synchronizing signals, the receiving machines will be automatically placed in synchronism. Or, the sending machine may be run continuously, sending out synchronizing signals, and the receiving machines started up at will and brought into synchronism automatically without stopping the sending machine.- In applications requiring two way operation, the direction of transmission may be quickly reversed without adjustment of the speed of either the sending or receiving machine, and without adjustments to compensate for line'or instrumental delays. Since the synchronizing signals are only required to operate a trigger device, such as a corrector magnet, the energy for actual correction being obtained from the drive means, relatively weak synchronizing signals maybe utilized. The synchronizing signals may be of the same order as the operating signals, and may be sent over the same channel as the operating signals. Likewise, the synchronizing signals are of suitable character to permit, transmission over any ordinary communication system. This is a point of practical importance in many applications, particularly where'radio communication channels are involved.

The system is equally applicable to machines having a common synchronous or independent power supply. Alternating current or direct current motors of uniform or substantially similar speed characteristics may be used as the drive means. When synchronous motors supplied from a common power source are used, the synchronizing apparatus functions to establish unison, and

the synchronous power from the common powersource thereafter maintains synchronism. since under normal conditions the drive motors will continue in synchronism indefinitely.

When drive motors are used that do not operate in accurate isochronism, as non-synchronous alternating current or direct current or other types of motors running at speeds relatively close to each other or substantially isochronously, the

synchronizing apparatus functions; 'to-. establish .and thereafter maintain synchronismfcompensating in the necessary manner for diiierences, either constant or variable, in the respective speeds. Furthermore, synchronizationmay also be accomplished where one motor operates at a multiple or sub-multiple speed with respect to the other. I c.

In event communication or thesupply of power the synchronizing apparatus 'functi matically reestablish synchronism.

Since the drive shafts at the sending and receiving machines run at the same speed when sending and receiving, and the phase corrector mechanism does not affect the speed of the driven member under normal conditions, the employment of the same mechanism for both'sending the printing telegraph example, the same rotary distributor may be used for both sending and receiving functions, and likewise the same rotary drum in the facsimile example may be used both claims.

What is claimed is: 1. In drive mechanism for rotary communication apparatus, a continuously rotating; drive shaft; a rotary member rotatably mounted thereon; means adapted to couple said rotary member to said drive shaft comprising a bell crank member aflixed to said rotary member, gear means driven by said driveshaft, a pinion rotatably mounted on one arm of said bell crank member and adaptedto mesh with said gear means, a

coupling member ailixed to said pinion, a pawl member pivotally mounted on a.secon'd arm of said bell crank member and adapted to engage said coupling member, means tending to effect such engagement; and means for checking and releasing said pawl member to control the motion of said rotary member.

2. The combination of claim -1 and means adapted upon selection to rotate saidv rotary member at the same speed as the drive shaft, or'

diflerentially with respect thereto.

3. In drive mechanism for rotary distributors,

a rotary contactor and fixed corrector contacts operatively associated therewith, driving. means for said contact'or, a plurality of epicyclic means adapted upon selection to cause said contactor to rotate at thesame speed, or at a differential speed, with respect to its drive means, and means controlled through said corrector contacts for holding said epicyclic means stationary, or for releasing said means selectively to effect predetermined differential correction of said rotary contactor.

4. In synchronizin apparatus, a drive shaft,

5 toautoadapted to be driven from said drive means, and

I gears.

, 7 a driven member, and driving means therebe- Y tween for selectively causing said driven member to rotate atthe same speed as the drive shaft, or differentially with respect thereto, said driving means including a plurality of coaxial gears 5 each arm and each meshing with a plurality of and receiving functions is facilitated. Thus in said gears of unlike number of-teeth, and-means 1 provided for selectively holding said arms stationary or providing for rotation thereof to ef fect selective control of the speed of rotation of said driven member with respect to said drive shaft. 1

5. In a gear system for synchronizing apparatus, a drive" shaft, a gear train mounted thereon comprising a drive gear fast to the drive shaft, an intermediate driving gear rotatably mounted thereon, a final driven gear similarly mounted,

' and means for causing the final driven gear to revolve at the same speed as, or slower or faster in predetermined amount than, the drive shaft including an epicyclic arm pivoted about said shaft and carrying gear means meshing with said 2 drive gear and said intermediate driven gear, a second epicyclic arm pivoted about said shaft ,and carrying gear means meshing with said intermediate driven gear and. said final driven gears, and control means adapted to control the move- 3 ment of said epicyclic arms. 6. In phase correcting mechanism, a gear' train including control means adapted upon selection thereof to produce a predetermined increase or decrease in the, speed ratio of a driven member 3 with respect to a drive member, comprising three main gear members with coincident axes, and two idler gearmembers mounted on separate epicyclic train arms pivoted about the coincident axis, and adapted to mesh in common with oneof said main gear members and individually with others of said main gear members.

7. In communication apparatus of the character described, a drive means, a driven member means establishing a driving connection between said drive means andsaichdriven member comprising a first gear driven from said drive means, a second gear in driving engagement with said driven member, a third sear having a number of teeth different from both said first and said second gears, and means for selectively coupling together said third gear with either said first or said second gears and including means for effecting a differential drive between said third 55 gear and the uncoupled one of said first or second HARRY J. mcnors. 

